The invention relates generally to the field of wind turbines, and more specifically to active flow modification in wind turbines for reducing loads, reducing aerodynamic losses, improving energy capture, reducing noise, and combinations thereof.
Wind turbines are increasingly gaining importance in the area of renewable sources of energy generation. In recent times, wind turbine technology has been applied to large-scale power generation applications. Of the many challenges that exist in harnessing wind energy, one is maximizing wind turbine performance while minimizing system loads in given wind conditions. Non-limiting examples of improved wind turbine performance parameters, which lead to minimized cost of energy, include maximized aerodynamic efficiency, maximized energy output, minimized wind turbine system loads, minimized noise, and combinations thereof. Examples of wind turbine system loads include extreme loads (operational and parked/idling) and fatigue loads.
In general, flow separation over wind turbine blades leads to stall, which is often a limiting factor in wind turbine blade design. When stall occurs, lift generated by the blade decreases significantly and a large component of the torque, which is the driving force imparted by the wind to the wind turbine, is lost. Solutions that provide an ability to control (diminish or delay) separation will allow the wind turbine blade to maximize lift. Some passive flow control solutions, for example, vortex generators, have been applied to remedy the boundary layer separation problem, but in such solutions there is no provision to stop the flow control when the flow control becomes unnecessary or undesirable. For example, one of the principal constraints in wind turbine design is that caused by system loads. When a separation control solution is being used to enhance lift, the blade experiences higher loading that can reach failure-inducing levels if the wind conditions change beyond normal operational or expected levels.
One effective approach for increasing the energy output of a wind turbine is to increase the swept area of the blades, for example, by increasing rotor size (diameter). The higher systems loads on a larger rotor (thicker and larger chord length) due to structural and material limitations, and blade/tower clearances typically constrain this growth. Another challenge is posed by changing wind conditions such as wind gusts or storms that lead to an undesired loading of the wind turbine blade as the lift being generated fluctuates or increases to very large levels. These loads constraints often lead to increased cost of the blade and other components of the wind turbine system, which can reduce or cancel the benefits of growing the rotor in terms of a system-level metric like cost of energy.
Another challenge that exists in harnessing wind energy relates to undesirable effects of the tip vortex generated by the wind flow at the tip of the blades. Besides causing energy harnessing losses, these tip vortices also lead to undesirable noise emanating from the tip end of the blade.